As means for obtaining color hard copies there have conventionally been studied color image recording techniques based on ink-jet, electrophotographic, thermal-transfer and silver halide photographic processes. Among these, particularly, the thermal-transfer process has the merits that its thermal-transfer recording material can be easily handled and maintained, its equipment can be made smaller in size for cost reduction, and its running cost is inexpensive.
In the thermal-transfer recording process, the dye used therefor plays an important role, but those conventionally used in the process have the disadvantage that the stability of images formed therewith is poor, particularly in the fixability and resistance to light.
In order to solve the above problem, JP O.P.I. Nos. 78893/1984, 109389/1984 and 2398/1985 disclose the use of thermally diffusible dyes capable of chelating (hereinafter called post-chelating dyes) to form a chelate dye image on an image-receiving material. JP O.P.I. No. 114892/1991 discloses a thermal-transfer recording material containing a post-chelating dye for forming a pyridylazo-type magenta dye and an image-forming method which uses the same dye.
The post-chelating dyes disclosed in the above patent publications have such excellent characteristics as the satisfactory color for forming satisfactory magenta color images, high chelating-reactivity, and high sensitizability. However, they have problems in their preservability when used in ink sheets and their aptitude (solubility) for the use in ink-making.